In recent years the field of telephony has been advanced through the use of solid state switching systems in which the signalling information is processed using integrated circuitry and computer technology.
An object of the present invention is to provide an improved signalling device for key telephone systems using CMOS (complementary-symmetry metal oxide semiconductor) digital detection which combines all counting and decoding functions in a single device. Another object of this invention is to provide an intercom signalling device which allows the connection of up to 19 intercom stations. Still another object of the invention is to provide an intercom signalling device which may utilize either single digit or two-digit codes. Still another object of the invention is to provide a device in which the calling signals can be repeated without the necessity of operating the switch hook on the telephone instrument. Yet another object of the invention is to provide a device which includes a one second signal contact closure whenever an intercom signal is detected. Yet another object of the invention is to provide a device which is so compact and self-contained that it may be installed in a fraction of the time and at less cost than prior art systems.